Double-sided indexable cutting insert and method of manufacture

ABSTRACT

A double-sided indexable cutting insert includes a top side and a bottom side interconnected by an edge surface. A plurality of upper major cutting edges are formed at a transition between the top side and the edge surface, and a plurality of lower major cutting edges are formed at a transition between the bottom side and the edge surface. Adjacently situated major cutting edges at each of the top and bottom sides are interconnected by corner cutting edges disposed along respective corners of the insert. Each corner cutting edge includes a minor cutting edge and a nose cutting edge. The nose cutting edge extends to the respective minor cutting edge from a respective major cutting edge. A portion of the edge surface disposed to one side of a bisector of each corner extends from a nose cutting edge of the top side towards a minor cutting edge on the bottom side and forms a downwardly facing step substantially midway between the top and bottom sides. A portion of the edge surface disposed to the other side of the bisector of the same corner extending from a nose cutting edge of the bottom side towards a minor cutting edge of the top side and forming an upwardly facing step substantially midway between the top and bottom sides.

FIELD OF THE INVENTION

The present invention relates to a cutting insert for chip removingmachining and a method for manufacturing the cutting insert.

BACKGROUND OF THE INVENTION

In tools for metalworking, indexable, asymmetrical inserts of hard andwear-resistant materials are used, such as cemented carbide or cubicboron nitride (CBN). There are a number of embodiments of cuttinginserts for use in only one feeding direction. These are usuallydenominated right or left hand inserts and comprise peripheries and/orchip breakers having an asymmetrical shape in relation to the bisectorof a cutting corner. These cutting inserts are adapted for only onefeeding direction.

Examples of indexable inserts having asymmetrical cutting corners areshown in U.S. Pat. No. 3,955,259, SE 517274 (corresponding to WO0047405), GB 1443743 and U.S. Pat. No. 3,229,349.

OBJECTS OF THE INVENTION

One object of the present invention is to provide a cutting insert thathas a plurality of feeding directions.

Another object of the present invention is to provide such an indexablecutting insert that only is of left or right hand design.

Another additional object of the present invention is to provide acutting insert, which can utilize both sides of the cutting insert forcutting.

Another additional object of the present invention is to provide anefficient method for manufacturing the cutting insert.

This is realized by a double-sided indexable cutting insert for chipremoving machining. The insert comprises a negative, generally polygonalbody having a plurality of cutting corners. The body has a top side anda bottom side interconnected by an edge surface. A plurality of uppermajor cutting edges are formed at a transition between the top side andthe edge surface. A plurality of major lower cutting edges are formed ata transition between the bottom side and the edge surface. Adjacentlysituated major cutting edges at each of the top and bottom sides areinterconnected by corner cutting edges which are disposed alongrespective corners of the insert. Each corner cutting edge comprises aminor cutting edge and a nose cutting edge. The nose cutting edgeextends to the respective minor cutting edge from a respective majorcutting edge. A bisector of each corner cutting edge intersects the nosecutting edge. Each corner cutting edge is asymmetrical with respect toits respective bisector. The nose cutting edge of each corner cuttingedge is defined by a first radius, and the minor cutting edge is definedby a second radius which is longer than the first radius. The nosecutting edges of the top side at least touch a common top plane. Thenose cutting edges of the bottom side at least touch a common bottomplane oriented parallel to the top plane. An imaginary line extendingperpendicularly to the top and bottom planes and intersecting the maincutting edge of any cutting corner at a location in-between oppositeends of such minor cutting edge, passes through the body.

The present invention also relates to a method of manufacturing adouble-sided, indexable cutting insert for chip removing machining froma plate of a hardware-resistant material. The plate has a thicknessdefined between top and bottom sides. The plate is of generallypolygonal shape defining a plurality of corners. The method comprisesthe steps of:

-   -   A) fastening the plate in a fixture;    -   B) machining a first corner of the plate along a portion thereof        extending from the top side for about one-half of the plate        thickness, to form a curved edge surface portion, and a top        curved corner cutting edge comprised of a top nose cutting edge        and a top minor cutting edge;    -   C) inverting the plate in the fixture to reverse the positions        of the top and bottom sides;    -   D) machining a remaining portion of the first corner to form        another curved edge surface portion, and a bottom curved corner        cutting edge comprised of a bottom nose cutting edge and a        bottom minor cutting edge, wherein the bottom nose cutting edge        is situated opposite the top minor cutting edge, and the bottom        minor cutting edge is situated opposite the top nose cutting        edge, and wherein an imaginary line which extends perpendicular        to top and bottom parallel planes that are touched by respective        top and bottom nose cutting edges, and which intersects either        of the minor cutting edges at a location in between opposite        ends of such minor cutting edge, passes through the plate; and    -   E) performing steps B and D on a second corner of the plate to        render the insert indexable.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the indexable insert according to the present inventionis described below, reference being made to the appended drawings,wherein;

FIG. 1 shows a planar view of a triangular indexable insert according tothe present invention.

FIG. 1B shows a cross-section of the indexable insert according to theline IB-IB in FIG. 1A.

FIG. 1C shows a cross-section of the indexable insert according to theline IC-IC in FIG. 1A.

FIG. 1D shows a cross-section of the indexable insert according to theline ID-ID in FIG. 1A.

FIG. 1B shows an enlargement of a cutting corner of FIG. 1A.

FIG. 1F shows the cutting corner in perspective view.

FIG. 1G shows the indexable insert in perspective view.

FIG. 2A shows the indexable insert during longitudinal turning in aworkpiece.

FIG. 2B shows the indexable insert during transverse turning in aworkpiece.

FIG. 2C shows the indexable insert while copying a workpiece on a lathe.

FIG. 3A shows a planar view of a rhombic indexable insert according tothe present invention.

FIG. 3B shows an enlargement of a cutting corner of FIG. 3A inperspective view.

FIG. 3C shows a cross-section of the indexable insert according to theline IIIC-IIIC in FIG. 3A FIG. 3D shows a cross-section of the indexableinsert according to the line IC-IC in FIG. 1A.

FIG. 3E shows a cross-section of the indexable insert according to theline IIIE-IIIE in FIG. 1A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The indexable insert 10 in FIGS. 1A-1G is intended for turning ormilling. The cutting insert, which is shown in right hand design, has asubstantially triangular basic shape and comprises a top side 11, abottom side 12, and three edge surfaces 13, which substantially connectsthe top and bottom sides 11 and 12, respectively. The cutting insert 10has a negative geometry, i.e. each edge surface 13 is perpendicular to aplane P, which coincides with the top side 11 or the bottom side 12,which means that the cutting insert has a substantially constantclearance angle around the cutting insert, also in the cutting corners.The cutting insert consists of sintered cemented carbide (for instanceWC+Co) or cubic boron nitride (CBN) or a combination of CBN and cementedcarbide where the cutting corners consist of CBN plates that are bondedat the corners. The top side 11 constitutes rake face and the edgesurface 13 constitutes edge surface. Upper major cutting edges 15A areformed at transitions between the top side 11 and the edge surfaces 13of the cutting insert. Lower cutting edges 16A are formed at transitionsbetween the bottom side 12 and the edge surfaces 13. Said sides 11, 12constitute a rake face in a position when the side 11 is active in chipforming machining and a support surface when the cutting insert has beenturned upside down. Each side 11, 12 comprises a planar surface, theperiphery of which may be provided with an edge strengthening chamfer14.

The cutting insert 10 has three cutting corners 17. Each cutting corner17 comprises a nose edge 18 and a minor cutting edge 19. The nose edge18 connects to the connected major cutting edge 15A and to the connectedminor cutting edge 19. The minor cutting edge 19, which also may becalled finishing edge or wiper, in turn connects to a non-associatedmajor cutting edge 15B.

The cutting corner 17 has a bisector B dividing the corner into equalparts (30 degrees each, in this case) in relation to the major cuttingedges 15A, 15B.

The bisector B intersects the nose edge 18, at both the top and thebottom sides 11, 12. Each cutting corner 17 is asymmetrical in relationto the bisector B in regards of the geometry of the edges 15A, 18, 19and 15B.

The nose edge 18 is curved and may be defined by a radius R1. The minorcutting edge 19 is curved and may be defined by a radius R2. The radiusR1 is smaller than the radius R2 of the minor cutting edge. The minorcutting edge 19 connects to the non-associated major cutting edge 15Bwith a radius R3. The radius R3 is smaller than the radius R2 of theminor cutting edge but larger than the radius R1.

Each side 11, 12 comprises three nose edges, which at least partly toucha plane P. The plane P is in this case parallel with both the top andthe bottom sides.

An imaginary line L (see FIG. 1C), which is perpendicular to the plane Pand tangent to the minor cutting edge 19, intersects the edge surface 13at a distance L1 from the minor cutting edge. The distance L1 equalsabout half of the thickness L2 of the cutting insert, FIG. 1G. The lineL coincides with the edge surface 13 for about half of the thickness L2of the cutting insert. The edge surface 13 has a step 20A, 20B on bothsides of the bisector of the cutting corner. The step 20A, 20B issubstantially parallel with the plane P. The step 20A, 20B forms a sharpcorner 21 with the edge surface 13 next to the step 20A, 20B in order toconstitute an indication of fracture that at a possible breaking of thecutting edge controls the breakage and keeps the lower part of thecutting insert intact.

A direction oriented, double-sided wiper insert having only 3 radii inthe cutting corner has the advantage that it is possible to form aradius or shoulder in a workpiece 30 to an exact geometry without theneed for compensation in the NC program, i.e. the cutting insert leavesthe workpiece having the same geometrical shape as a standard turninginsert having a nose edge according to the ISO standard. This at thesame time as the cutting insert has a wiper effect at longitudinalturning. i.e. the cutting insert leaves the workpiece having the samegeometrical shape as a standard turning insert having a nose radiusaccording to the standardized norm. Furthermore, a cutting insert formedin such a way provides lower radial cutting forces, which is desirableat generation of fine surfaces, than a traditional wiper insert having 5radii after each other.

Thus, the invention aims at getting away from this type of problem byforming only half of the thickness, and thereby obtaining a double-sidedwiper insert that only is of left or right hand design. The step 20A,20B protects the subjacent edge in an effective way. Since the cuttinginserts are expensive, such as CBN inserts, the operator often machinestoo long. Without a wiper, this entails numerous measurement correctionsin the turning lathe. The CBN insert maintains the measurements well,even after considerable wear. Finally, it breaks down. The indexableinsert according to the present invention ensures that the cutting edgebelow is protected.

FIG. 2A shows the indexable insert at longitudinal turning of theworkpiece 30 with the feeding direction according to the arrow in FIG.2A. FIG. 2B shows the indexable insert 10 at transverse turning of theworkpiece 30, wherein the minor cutting edge substantially does notmachine the same. FIG. 2C shows the indexable insert during copying ofthe workpiece 30 on a lathe.

In all the machining examples, the cutting insert has been mounted ininsert holders with a setting angle of 93°, and a clearance angle andminor insert angle of 6° each.

The indexable insert 10 is manufactured in the following way. Apolygonal plate of a hard wear-resistant material such as CBN, having athickness L2 and equally large side surfaces, is fastened in a fixture.The edge surfaces are ground over the entire thickness in a conventionalway. At least a first corner portion is machined, preferably by means ofgrinding, so that a first area, corresponding to approximately half thethickness, obtains a rounded nose edge 18 and a minor cutting edge 19.It is suitable to perform the corresponding machining on the othercorner portions of the plate and then turn the polygonal plate upsidedown 180°. The plate is fastened in the fixture again in order tomachine some of the corner portions, at least the first corner portion,preferably by means of grinding, so that a second area, corresponding toapproximately half of the thickness, obtains a rounded nose edge 18 anda minor cutting edge 19. Then, it is advantageous to machine the noseedge 18 so that it obtains a radius R1 that is smaller than the radiusR2 of the minor cutting edge. It is most suitable to grind all cornerportions of one of the halves in one set-up.

The indexable insert 10′ in FIGS. 3A-3E is intended for turning ormilling. The cutting insert has a substantially rhombic basic shape withtwo cutting corners 17′ and four cutting edge portions. Equally indexedreference numbers designate equal details mentioned above. What makesthis cutting insert 10′ different from the above-described cuttinginsert 10, in addition to the basic shape, is the shape of the edgesurface 13′ in the cutting corner 17′. This cutting insert 10 isinjection-molded or directly pressed and the edge surface 13′ in thecutting corner has a continuous or stepless transition between theopposite cutting edges in a cutting corner. The cutting corner 17 has anose edge 18′ and a minor cutting edge 19′. The nose edge 18′ connectsto the associated major cutting edge 15A′ and to the associated minorcutting edge 19′. The minor cutting edge 19′ in turn connects to anon-associated major cutting edge 15B′. An imaginary line L′, which isperpendicular to the plane P′ and tangent to the minor cutting edge 19′intersects the edge surface 13′ according to FIG. 3D. A line,corresponding to the line L′, which is tangent to both of the nose edges18′, runs at a distance from the centre of the edge surface 13′, in theplane of the bisector B, according to FIG. 3C. In the illustratedcutting insert 10′, the edge surface 13′ is concave.

Furthermore, the cutting insert 10′ has a through hole intended toreceive a fixing screw (not shown), which fixes the cutting insert 10′to the insert holder.

Thus, the present invention relates to an indexable, asymmetricalcutting insert, which is of only left or only right hand design thatpermits utilization of both sides of the cutting insert for machining inthe same direction. Furthermore, an efficient method for manufacturingthe double-sided cutting insert is provided.

The invention is in no way limited to the embodiment described above,but may be varied within the scope of the appended claims. The cuttinginsert may have another polygonal basic shape, such as a square,rectangular, pentagonal, hexagonal or octagonal basic shape. The cuttinginsert 10 may be provided with a through hole intended to receive afixing screw.

1-10. (canceled)
 11. A double-sided indexable cutting insert for chipremoving machining; the insert comprising a negative, generallypolygonal body having a plurality of corners; the body having a top sideand a bottom side interconnected by an edge surface; a plurality ofupper major cutting edges formed at a transition between the top sideand the edge surface; a plurality of lower major cutting edges formed ata transition between the bottom side and the edge surface; adjacentlysituated major cutting edges at each of the top and bottom sides beinginterconnected by corner cutting edges disposed along respective cornersof the insert; each corner cutting edge comprising a minor cutting edgeand a nose cutting edge; the nose cutting edge extending to therespective minor cutting edge from a respective major cutting edge; abisector of each corner cutting edge intersecting the nose cutting edge;each corner cutting edge being asymmetrical with respect to itsrespective bisector; the nose cutting edge of each corner cutting edgedefined by a first radius, and the respective minor cutting edge definedby a second radius longer than the first radius; the nose cutting edgesof the top side at least touching a common top plane; the nose cuttingedges of the bottom side at least touching a common bottom planeoriented parallel to the top plane; wherein an imaginary line whichextends perpendicular to the top and bottom planes and which intersectsthe minor cutting edge of any cutting corner at a location in-betweenopposite ends of such minor cutting edge, passes through the body. 12.The cutting insert according to claim 11 wherein the imaginary lineintersects the edge surface at a location substantially midway betweenthe top and bottom surfaces.
 13. The cutting insert according to claim12 wherein the imaginary line coincides with the edge surface until itintersects the body.
 14. The cutting insert according to claim 11wherein a portion of the edge surface disposed to one side of thebisector of each corner extends from a nose cutting edge of the top sidetowards a minor cutting edge on the bottom side and forms a downwardlyfacing step substantially midway between the top and bottom sides; aportion of the edge surface disposed to the other side of the bisectorof the same corner extending from a nose cutting edge of the bottom sidetowards a minor cutting edge of the top side and forming an upwardlyfacing step substantially midway between the top and bottom sides. 15.The cutting insert according to claim 14 wherein each step issubstantially parallel to the top and bottom sides.
 16. The cuttinginsert according to claim 15 wherein each step forms an angle ofsubstantially ninety degrees with the imaginary line.
 17. The cuttinginsert according to claim 11 wherein the edge surface forms a clearanceangle with each of the top and bottom sides, the clearance angles beingconstant around the periphery of the insert.
 18. The cutting insertaccording to claim 11 wherein the entire insert comprises cubic boronnitride (CBN).
 19. The cutting insert according to claim 18 wherein theinsert comprises a combination of cubic boron nitride (CBN) and cementedcarbide, with the cutting corners comprised of brazed-on CBN plates. 20.A method of manufacturing a double-sided, indexible cutting insert forchip removing machining from a plate of a hard wear-resistant materialhaving a thickness defined between top and bottom sides, the plate beingof generally polygonal shape defining a plurality of corners, the methodcomprising the steps of: A) fastening the plate in a fixture; B)machining a first corner of the plate along a portion thereof extendingfrom the top side for about one-half of the plate thickness, to form acurved edge surface portion and a top curved corner cutting edgecomprised of a top nose cutting edge and a top minor cutting edge; C)inverting the plate in the fixture to reverse the positions of the topand bottom sides; D) machining the first corner along a remainingportion thereof to form another curved edge surface portion, and abottom curved corner cutting edge comprised of a bottom nose cuttingedge and a bottom minor cutting edge, wherein the bottom nose cuttingedge is situated opposite the top minor cutting edge, and the bottomminor cutting edge is situated opposite the top nose cutting edge, andwherein an imaginary line extends perpendicular to top and bottomparallel planes that are touched by respective top and bottom nosecutting edges, and intersects either of the minor cutting edges at alocation in between opposite ends of such minor cutting edge, theimaginary line passing through the plate; and E) performing steps B andD on a second corner of the plate to render the insert indexible. 21.The method according to claim 20 wherein the machining in steps B and Dcomprises grinding.
 22. The method according to claim 20 wherein steps Band D further comprise forming the top and bottom nose cutting edgeshaving a first radius and forming the top and bottom minor cutting edgeshaving a second radius longer than the first radius.